This invention relates to the field of air conditioning and cleaning and, more particularly, to improved indoor air cleaning methods and systems for compliance with National Indoor Air Quality Standard ANSI/ASHRAE 62-1989.
The World Health Organization furnishes data showing measured levels of up to 0.4 mg/m3 of ozone and 1.0 mg/m3 for NO2 in workplace indoor air which is well over the acceptable limits for ozone and approaching acceptability level for NO2. When one considers the known ability of commonplace office equipment to produce such gases through the ionization of air within the equipment, one can readily appreciate that improvements in indoor air cleaning are needed to meet the levels set forth in the Standard.
Those familiar with the production of ozone for commercial purposes are aware that in addition to ozone the equipment also produces nitrogen oxide and nitrogen dioxides through the same ionization process which produces ozone. It is equally well known that electronic equipment, which has become so common to the office worker environment, produces ozone in a similar fashion as the IEEE requires certification that equipment produced according to it protocols is certified to emit no more than 0.1 ppm of ozone.
The invention disclosed herein is a two stage air cleaner configured to control levels of both ozone and nitrogen dioxide concentrations where such air contaminants are propagated within the workplace to preclude substantially degradation of indoor air quality provided by HVAC (heating-venting-and air conditioning) systems. These pollutants are known to be propagated through the use of electronic equipment and operations which ionize air within workplaces which use such equipment.
The invention operates in a unique sequential manner upon air induced through its intake section wherein water droplets are initially intimately mixed with contaminated air, to absorb any soluble nitrogen dioxide conveyed within the airstream and then, once the air has been suitably mixed into a drier, but higher humidity controlled condition, through the evaporation of all free moisture suitable to react its ozone content. Continuous mixing, as taught herein, in a mariner which assures adequate molecular contacts between ozone and molecular water for a gas-to-gas phase reaction to replicate a process known to quench ozone. Hence, ionized gas contaminants of an air stream traveling through the inventions envelope specifically engineered to assure the transfer of the electronic charge of the ionized gases to the grounding path which the invention""s enclosure provides is cleaned of the cited pollutants.
This two step air cleaning process is new art uniquely created to satisfy the ANSI/ASHRAE 62-1989, Indoor Air Quality Standard which governs what is, and is what is not acceptable workplace air quality with respect to the ionized gases produced within the workplace, which otherwise would render that air unsuitable for recirculation through standard HVAC (heating-ventilating and air conditioning) system configurations. ASHRAE 62-1989, the American Society Of Heating, Air Conditioning and Refrigeration Engineers, is the peer group professional society charged with responsibilities for establishing standards of practice for those who design, construct, maintain and manage buildings.
The ANSI/ASHRAE 62-1989 Standard publishes limits for commonly known building pollutants, as concentrations listed within its Table C-1, lists the ozone and nitrogen dioxide permissible exposure limits along with many other potential pollutants. FIG. 1, as reproduced from the Standard shows possible locations to which an air cleaning device may be applied. The alternate methodology for controlling pollutants specified within the Standard relies on increasing ambient air rates to purge pollutants to the acceptable levels through dilution. The invention applies the principles of air cleaning only to the return air cleaning task as the most effective way of achieving compliance with the Standard with respect to the ionized gases which have been cited as common to workplace usage.
FIG. 1 also illustrates an occupancy wherein a source generates a pollutant and how the invented return air cleaner is applied to mitigate, or otherwise remove the pollutants to preclude the reintroduction of the contaminated air back into the occupancy. While the invention is one of many air cleaners which might be applied, it is specific only to ionized gases as previously cited. Without application of the invention, not only would the source emissions increase, but any recycled ones as well, through cycles-of-concentration. Cycles-of-concentration result from the recirculation of HVAC system air operated to minimize the costs associated with heating and cooling the large air masses required to comfort condition and ventilate workplaces served by central HVAC systems.
Hence, the return air cleaner, as set forth herein, will react the ionized gases out of the return air stream which acts to zero-out the complex cycles of concentration component of the indoor air ability equations of Appendix E of the Standard.
While the invention deals with nitrogen dioxide, a primary focus is on the ozone which invariably accompanies nitrogen dioxide, both gases being formed from an ionization process and not products of combustion which are considered the usual source of nitrogen dioxide. Current OSHA labor law cites ozone at 0.1 ppm as the TWA exposure limit. Nitrogen dioxide is similarly limited to 5.0 ppm at present. Hence, control of ozone level is one of the invention""s primary objectives because the World Health Organization has published detection levels of up to 0.2 ppm of ozone measured as a building air quality pollutant.
ASHRAE has documented that ozone propagation is directly related to the concentration of water molecules which act to inhibit the ionization process as have the manufacturers of commercial ozone generators and these have provided key factors in developing the invented return air cleaner.
The invented return air cleaner acts to control ozone levels in a two fold manner. First, by inerting the ionized gases traveling through the return-air-cleaner (RAC). A direct control mechanism. Second, by reducing the propagation rate of the electronic equipment located within the occupancies through the elevated moisture content of the substantial recirculated air component which has been mixed with ambient ventilation air in accordance with the teachings of the Standard itself. An indirect control mechanism.
It is the sum total of both of these effects which is needed to control the level of ozone within the workplace served by the HVAC system within which the return air cleaner is applied.
In general the commercial and industrial HVAC systems in use today circulate a thermally conditioned air stream composed of 75 to 80% recirculated air and 20 to 25%, ambient air sourced ventilation air. This invention is particularly suitable to upgrade such HVAC systems for compliance with ANSI/ASHRAE 62-1989 by controlling cleaning rates to what are the currently documented safe occupancy exposure levels of these gases. Hence, the invention disclosed herein is a return air cleaner applied in accordance with the teachings of the Standard which can become the optimum technology to satisfy the requirements of the Standard. Cleaning the air from office type occupancies by making it safe for recirculation in quantities of about 80% of the entire air mass distributed by the HVAC systems to maintain safe and healthy workplaces with acceptable indoor air quality as defined by the ANSI/ASHRAE Standard with respect to ozone.
The invented RAC is the alternate technology to dilution ventilation which can be energy intensive as compared to working with the respective dilution rate formulas of the Standard. Such comparison reveals that a RAC application substantially diminishes ventilation rates to those established within the Standard and promises to be the most cost effective solution to mitigating pollutants which result from the ionization of air into the hazardous gases listed in Table C-1.
In examining Table C-1, of particular concern are nitrogen dioxide and ozone which are specified as safe at relatively low concentrations with 5 ppm and 0.1 ppm being the respective limiting values. In June of 1997, ozone limits were lowered by the EPA from the cited 0.1 to 0.08 ppm and it can be anticipated that ANSI/ASHRAE 62-1989 will adopt this lowered limit, as the Standard speaks to acceptable indoor air quality being no worse than that of the ambient.
Since the EPA proposed even lower levels than its 0.08 ppm ozone xe2x80x9ccompromisexe2x80x9d value, the need exists and the invention provides for complying with ever reduced limits for ozone within breathing/breathable air within the manufactured environment provided by central HVAC systems.
The invented RAC-FOG equipment provides for necessary variation in compliance levels as it incorporates sense and feed back controls which enable it to control ozone removals from an air stream to an addressable setpoint as measured within the occupancy wherein ozone propagation rates vary and within the ducting downstream of the RAC unit exit. In this manner the invention can respond to the wide range of variables affecting both the psychometric and usage variables related to the propagation of ozone, as well as any ambient air ozone pollutants which could increase in concentration through recirculation.
The use of the invented RAC (return air cleaner) as a gas to gas phase cleaner is needed because at present there is no commercial, at market cleaner which can deal effectively with both of these gases other than charcoal absorption. Hence, a need has arisen to devise one which can deal equally well with both of these gases and thusly meet the needs of the return air cleaning task ANSI/ASHRAE 62-1989.
Ozone is a molecule consisting of positively charged oxygen atoms and is rapidly quenched by the concentration of water in its molecular (gaseous) state. Sustained molecular impacts between the gases quickly bleeds down the charge carried by the unstable ozone molecule and with well established ground paths through the unit housing can quickly react the ozone our of the air stream.
While ozone is relatively insoluble with respect to water, it decays in direct proportion to the concentration of water molecules within the overall air volume of the air/ozone/water molecule mixture propagated within the units mixing zone. This is a gas-to-gas phase reaction which will react all ozone molecules once the concentration rises above the 80% of saturation water vapor concentration as demonstrated by both ASHRAE research and by those who have observed the quick vanishing of ozone propagated during thunderstorms.
The ozone production industry furnishes an ionization constant of 93 xcexc/watt-hour for ozone production within very dry air. Conversely, virtually no ozone output occurs in air at 80% of air stream saturation, at saturation temperature molecular water vapor concentrations. ASHRAE teaches that the relationship between these cited endpoints is linear. Hence, the invention which moistens air on an ETD (evaporation-to-dryness) basis, to a moisture content of at least 80%, which defines RH (relative humidity) came to be made.
NO2 (nitrogen dioxide), is produced through an ionization constant of 167 xcexcgm/watt-hour under similar circumstance. NO2 is well known to react upon contacting water into nitric acid. That reaction is instantaneous. While a gas to gas reaction also occurs, as is well documented in the formation of acid rain within ambient air, this reaction is a much slower hydrolysis reaction. Hence, a mechanism which forces mixing, or an equivalent wetted impaction surface film, to cause intimate contact between NO2 gas molecules and water, which is a requirement for the RAC invention. An air cleaner which provides a contact water surface as either a film or droplets will capture NO2 out of the airstream and into the water as dilute nitric acid, or in the case of an atomized liquid humidification process, nitric acid vapor is left airborne, after the water content of the droplet as evaporated, is new art with respect to HVAC applications.
When a water supply with even a relatively small or low hardness (alkalinity from dissolved minerals normally calcium or sodium, complexed ions) as in common to almost any municipal domestic water source, is used the alkalinity of the evaporating water droplet increases as the third power of the evaporating droplet radius. Hence, the alkalinity of the droplet grows very rapidly and with rising pH precipitates what was the nitric acid component of the water droplet into a post evaporation nitrate, xe2x80x9chumidifier dustxe2x80x9d, in the presence of adequate mixing, as provided for within the invention. Such humidifier dust particulates are readily captured by filters, within the efficiency range specified by ASHRAE 62-1989 as required for use within the air handler of FIG. 1. Thus the return air cleaner (RAC), invented herein, need have no internal filters of its own.
The essentials of the invented RAC, as applied to its task of return air cleaning requires a sequential arrangement of its two stages packaged within a single housing to be inserted within the ducting which connects an occupancy with its heating, ventilating and air conditioning unit through its air return path.
Stage One, is a moistening and mixing process which assures that the entering contaminated air stream carrying ozone and NO2 is intimately mixed with water droplets or impacted upon a water film, both being well known for air stream scrubbing processes, for conversion of the NO2, a gas into HNO3, nitric acid, a liquid dissolved within water which is readily capturable. This is a liquid to gas reaction phase which captures highly soluble NO2 but does nothing for the insoluble ozone.
Stage Two, evaporates any water into its gaseous phase by thoroughly mixing droplets, or scrubbed air, into the receiving air stream to disperse uniformly, so that the water molecule concentration is adequate to assure contacting virtually all ozone molecules and achieve the ozone quench point molecular moisture ratio adequate for this purpose. This is the gas to gas reaction phase.
At exit, the leaving air is sensed with respect to its NOx content. NOx, a name applied to the multiple oxides of nitrogen, measurement is selected as the most practical method of determining ozone content, as direct measurements of ozone are very costly due to the oxidation potential of that gas. NOx is a simple, cost effective a reliable method of determining ozone produced by ionization of air. Reference is made to the respective ionization constants for these gases as a watt hour of ionization power will produce both 52 mg of ozone and 115 mg of nitrogen dioxide subject to the moisture content of the air being exposed to ionization radiation, or an electrostatic field.
Hence, any sensed nitrogen dioxide value read in ppm can be converted to an ozone concentration values by simply multiplying the NOx value by 93/167, equal to 55%. As an example, a NOx reading of 2 ppm will be converted to a 1.1 ppm ozone concentration.
Products of combustion from the introduction of contaminated ambient air might distort the measured value to create an artificially larger value of ozone. However, operating the invention with a NOx value which sets a larger ozone value errs on the side of safety becomes a desirable error as the incidental conversion of NO2 to acid equally deals with SO2, which frequently accompanies NO2, as a product of combustion on the same acid formation basis.
While the invention is configured on a stand alone basis using the described NOx sensor algorithm, with exit levels of sensed gas as its operational setpoint, it is equally amenable to function upon receiving the output of other sensors which might reduce its operating costs.
Experimentation has shown that at controlled water molecule concentrations the contiguous molecular impacts between ozone molecules and water molecules permit the charge required to maintain the ozone molecule to bleed down through the grounded sheet metal enclosure which constitutes the geometry of a fog absorption chamber. Hence the invention encloses all of its components within a totally conductive metal panel housing which is grounded through not only its water feed line but the solid pressurized water column within the feed piping to assure the grounding path at lowest possible potential.
While 100% removal efficiency is virtually impossible the invention is controlled to setpoints which will meet the most stringent environmental regulations.
The successful performance of both stages are dependent on high rate mixing within each stage. While more classic industrial process equipment can be applied to these tasks, most of the scrubbing equipment is highly resistive to the flow of air and requires significant energy inputs which are not normally applicable to HVAC equipment. The separation of the two phases of cleaning into two low energy processes, as taught herein, makes the overall mechanical energy input to support these operations acceptably low. Hence, optimum for RAC service and advantageous with respect to what the HVAC industry offers as the alternate, dilution ventilation with high rates of ambient ventilation air. The invention becomes very energy use effective when compared to the annual heating and cooling costs of excessive quantities of cold or warm ambient air thermally conditioned to be introduced as make-up air applied to preclude the cycles-of-concentration accumulation of the cited contaminants of concern.
The ability of the invention to cool the return air flow being cleaned adequately meets the ASHRAE definitions of a xe2x80x9cwatersidexe2x80x9d economizer and ASHRAE Standards also require that central HVAC systems include either a water, or air side economizer cycle to meet its energy use specifications.
The problem of airside economizer stratification for which many known xe2x80x9cdestratifiersxe2x80x9d are available, is dealt with in the present invention by cooling the larger return air mass which dramatically reduces the quantities of cold ambient air which would otherwise be required for economizer cycle service.
The invention configured herein is a RAC with contaminated air removed from the occupancy of FIG. 1 functioning in the illustrated return air position and processed through a chamber which evaporates a controlled quantity of water into an air stream to react the ionized gases of concern which result from the operation of equipment (sources, per the language of the Standard) within the occupancy. Return air so treated can be returned for filtration and thermal conditioning within the system air handler unit and be reused to ventilate and adequately maintain a safe and habitable indoor air quality with acceptable levels of O3 and NO2, in accordance with the narrow range limits specified for compliance with the Standards tabulated values. Habitable, as defined by the Standard, also includes temperature control of the workplace which is specified as a 70 degree F. winter minimum and 78 degree F. summer season maximum with an accompanying 30% minimum to 60% maximum controlled humidity.
Within the RAC itself, a wide variety of mixers and moisteners can be applied to accomplish the unique tasks which compliance with the Standard entails.
These can be:
1. Wetted media, in the form of corrugated tray type fill, as commonly applied in cooling towers, although a wide variety of industrial packings (Rasching Rings, Saddles, etc.) could be applied equally well, as air saturation media as per FIG. 2 and its identified internal components.
2. Atomizers and/or spray nozzles with secondary target surface evaporators per FIG. 3, which add a dampered method for controlling leaving humidity and enhanced mixing characteristics for the gas to gas ozone reaction phase. Mechanical atomizers, spin discs or similar swirl centrifugal atomization mechanisms can be applied in a configuration very similar to that of FIG. 3.
3. UFG""S ultrasonic fog generators utilizing electronic transducers per FIG. 4 equipped with the control and mixing appurtenances of FIG. 2, for the required two phase cleaning of the through putted air stream.
4. Two phase, compressed air and water fed UFG""s which use compressible flow principles to propagate high frequency oscillations which shatters water into ultrafine droplets per FIG. 5, but require no additional appurtenances for mixing and humidity control, the UFG""s being high rate mixers and controllable with respect to a variable fog propagation rate.
Within FIGS. 2, 3, 4 and 5 are included the means for moisture addition, mixing and humidity control as required to meet the gas cleaning objective of the invention. All of these figures show devices which will respond to sensed gas signals by varying water feed rates and/or bypass dampers to accomplish the gas cleaning aspects of the invention.
While saturated air can be propagated and distributed, it should be understood that saturated air is unstable and subject to condensation which ASHRAE defines as a likely biofilm hazard problem. One can cite the commonly observed phenomenon of the tops of buildings being shrouded in mist while ground level is moisture free, as defining just how even a very small reduction in pressure allows free moisture to form. Hence, the invention must operate through its sense and control network to control exit humidity to a below saturation level to preclude the cited free moisture formation to avoid any downstream condensation which would form bio/film hazards. A biofilm hazard is defined as one which could provide a site for biological pathogens to colonize and propagate allergens and toxins which could be entrained and broadcast within the ventilation air stream.